A hoisting and lowering apparatus, e.g. according to European patent publication EP-A-0 480 117 of the applicant, are preferentially used for the purpose of raising or lowering persons or loads on a rope. Preferred fields of application are rescue operations or generally the mobile application of such apparatus. Essentially, the hoisting/lowering apparatus have the function of reducing the retention force in the lowering operation, combined with a safety against an uncontrolled fall of the person or load suspended on the rope.
It has been found that the known hoisting/lowering apparatus should be variably equipped according to the actual conditions of application. For example, it should be possible with the hoisting/lowering apparatus to form a lifting block, or a possibility for the attachment of a spring hook etc. is required. However, in known hoisting/lowering apparatus, some of these different options have mutually excluded each other or, if designed for maximum functionality, they have led to an unconveniently large and heavy appliance.
Also, as the case may be, the use of a hoisting/lowering apparatus which is not adapted to the actual conditions of application can lead to an overload of the rope as well as to safety risks due to a possible overload of the safety devices of the hoisting/lowering apparatus. The consequences are the need for a premature replacement of the rope and the risk of rupture of the rope and of malfunctions of the appliance.
Usually, these known hoisting/lowering apparatus include a large-volume pulley having a large volume which is provided with a return stop. In most cases, a rope is wrapped 21/2 times around said pulley. In operation, the pulley is running freely during hoisting and offers little resistance. In descending, however, the pulley is blocked by the return stop, and the rope slides over the surface of the pulley. The resulting friction takes up the greater part of the load suspended on the rope.
Furthermore, an emergency stop for the rope is often provided on the load the of the pulley. Essentially, said rope stop senses the running speed of the rope particularly in the descending direction. In the case of an excessive speed, the rope stop is released and directly blocks the rope.
However, in practice, the known hoisting/lowering apparatus of this type cause a considerable wear of the rope by overcrossing windings on the pulley, in the passage of the known emergency stop, and especially when the latter is released. This wear reduces the resistance of the rope and the action of the emergency stop may cause a rupture of the rope, and the function of the hoisting/lowering apparatus is impaired since the frictional resistance on the pulley is altered.